In recent years, data is transferred between racks, boards, and inside a board at a higher rate than ever. This increase of the transfer rate depends on significant increases in the performance of a central processing unit (CPU) provided in a high-end server. Therefore, the technology of increasing the rate of data transfer performed with electrical wiring is approaching its limit, and an optical interconnect technology which allows for transferring data at a much higher rate is expected.
For achieving a higher rate optical interconnection, a light-emitting element should also be driven at a higher rate. When the light-emitting element is driven by a rectangular-wave signal, an optical output waveform illustrated in FIG. 1 is obtained, where the rise and fall of the optical output waveforms are asymmetrical. The lateral axis of FIG. 1 represents time and the vertical axis represents signal power. A time slot assigned for one bit of data is illustrated in FIG. 1.
For reducing the asymmetry of the rise and the fall of the waveform of the light-emitting element, for example, a driving circuit being in a semi-driving state outputs, in advance, signals which are smaller than those output from the driving circuit being in a driving state when a state of the display element is changed from the turn-off state to the turn-on state. Further, for changing the state of the display element from the turn-on state to the turn-off state, the driving circuit outputs, in advance, signals which are larger than those output from the driving circuit being in a non-driving state (for example, Japanese Laid-open Patent Publication No. 1-179194).
Further, the method of adjusting the brightness of a light-emitting diode (LED) by adjusting the current flowing through the LED in a step-like manner is disclosed in Japanese Laid-open Patent Publication No. 2009-277514, for example.
An LED driving circuit disclosed in this Patent Document includes a first peaking current generating circuit and a second peaking current generating circuit. After adding a first peaking current supplied from the first peaking current generating circuit to a driving current flowing through an LED, a second peaking current supplied from the second peaking current generating circuit is further added to the driving current flowing through the LED. The above-described method is disclosed in Japanese Laid-open Patent Publication No. 2006-40975, for example.